Fuller

[yud]

I have herd that the fuller is used to lighten the blade, but i just herd the "blood groove" story once more so which is it

[Gareth]

When it comes to swords the idea of a "blood groove" is nonsense, as you say it's about removing metal and giving some shape to the cross section of the blade.  I can only assume it's the same for other blades as well.

[Mike, Lord of the Spammers!]

It actually makes the blades a hell of a lot stronger, as it allows them a greater degree of flex before breaking

The fact that it lightens them is just a happy coincidence

[Magnus]

as others have said, it is about lightening the blade, and I would imagine, in eras gone by where steel was extremely precious, saving material.